1. Field of the Invention
The invention is related to a method and a device for stacking flat articles, in particular for stacking printed products.
2. Description of Related Art
It is known to deposit printed products in stacking shafts or in a similar device for the purpose of producing stacks of printed products. Such devices usually comprise a bottom and guide walls standing vertically on the bottom and they are open on the top for the supply of the printed products. In order to reduce to a minimum the free fall of the printed products during stacking, the position of the bottom or of the supply system is often adapted to the height of the stack already present in the shaft, so that every printed product can be slid substantially horizontally onto the previously deposited printed product or onto the shaft bottom.
For producing cross stacks, in which the printed products are stacked in layers or product groups each respectively rotated by 180xc2x0 relative to one another, for example, the bottom of the stacking shaft is designed for being rotated, and at least one intermediate bottom, which is removable from the shaft, is provided. Whenever a product group has been deposited, the bottom with the groups already stacked on it is rotated by 180xc2x0 while the printed products for the subsequent product group are being stacked on the intermediate bottom. When the bottom with the stack is again positioned after rotation, the intermediate bottom, if so required, is lowered into the stacking shaft and is then pulled out of the shaft so that the printed products stacked on the intermediate bottom are deposited on the rotated stack.
When a stack is completed, parts of the vertical guide walls or shaft walls are removed, if so required, and the stack is pushed out of the stacking shaft, usually transverse to the supply direction (or transverse to its projection onto the plane of the stacking shaft bottom, respectively) or in the supply direction. During the whole pushing-out process, the supply has to be interrupted or printed products being supplied have to be pre-stacked on the intermediate bottom.
In many cases, the supply stream is split-up to supply two stacking shafts such that while printed products are being supplied to one shaft, a finished stack is being pushed out of the other stacking shaft.
From the above brief description of the stacking processes as known in the printing field, it is evident that, for their implementation, particularly with high performance capacities or with short cycle times, respectively, rather elaborate devices are necessary. Such elaborate devices require a lot of space.
It is an object of the invention to create a method for stacking flat articles, which may be implemented with very simple devices and in little space while still allowing high unit processing capacities. It is a further object of the invention to create a device for carrying out the method according to the invention.
In accordance with the invention, the flat articles are supplied to the stacking shaft lying loosely on a supply support or else held clamped between two supply supports, for example in an imbricated formation with the leading edges positioned on the top of the formation. The supply support is, for example, a conveyor belt that brings the articles at an inclination from above toward a supply side of the stacking shaft and advantageously to a position just above the stacking shaft, where the supply support ends. The flat articles are driven by the supply support beyond the end thereof and against a side of the stacking shaft disposed opposite the supply side. The flat articles from the supply support into the stacking shaft at the latest, when their leading edge has reached the opposite side of the stacking shaft.
The completed stacks are pushed out in a pushing-out direction opposite to the supply direction (pushing-out direction opposite to the projection of the supply direction onto the plane of the stacking shaft bottom), i.e. through the supply side of the stacking shaft. For the pushing operation a per se known pusher is used. The pushing movement of the pusher starts at the side opposite the supply side of the stacking shaft and is directed toward the supply side. For returning the pusher back to its starting position, the pusher is moved outside of the stacking shaft, for example, underneath the stacking shaft or besides the stacking shaft.
The article supply is interrupted for a first part of the pushing movement. However, the supply can be resumed as soon as the trailing side of the pushed stack has passed the one point in the stacking shaft, at which a further supplied article comes into contact with the stack to be pushed out, i.e., at which this article would come into conflict with the stack. The article supply does not have to be interrupted for at least as long as the complete pushing operation takes as is necessary with known stacking methods; only a fraction of this time is sufficient. Therefore, stacking with the method according to the invention allows shorter cycle times or a higher capacity, respectively, and/or it allows shorter supply interruptions or less buffered articles, respectively, which means easier handling than is the case with known stacking methods.
The supply interruption necessary for the pushing-out becomes shorter, the more steeply from above supply takes place and the longer a free fall into the stacking shaft, i.e. a fall not guided by the supply support, can be tolerated. Because articles having a greater inherent stiffness can still be stacked well after a longer free fall than more flexible articles, the method in accordance with the invention is particularly adapted for stacking stiffer articles. If the method according to the invention is used for folded printed products, these are advantageously supplied to the stacking shaft in a direction parallel to their folded edge (i.e., for tabloid newspapers with a single fold or for newspapers folded twice: in longitudinal direction), because these products have a significantly greater stiffness parallel to the folded edge than transverse to it. Such supply provides the further advantage, that pushing-out of the stack is directed also parallel to the folded edge, i.e. in the one direction, in which stack stability for folded printed product stacks is greatest.
The method in accordance with the invention is therefore suitable in particular for stacking folded printed products, wherein the products are supplied parallel to their folded edges and the stack is pushed out in the opposite direction, once again parallel to the folded edges. For producing cross stacks, the printed products advantageously are supplied in an imbricated stream with alternating groups of correspondingly oriented products, wherein for supply interruptions the imbricated stream comprises gaps or the printed products are temporarily stopped or dammed.
The device for carrying out the method according to the invention comprises a stacking shaft and a supply support leading from above at an incline towards the supply side of the stacking shaft and ending above the opening of the stacking shaft (directly at the supply side or between the supply side and the opposite side). Furthermore, there is a pushing means that is movable through the stacking shaft in a pushing direction opposite the supply direction and returnable into its starting position on the side of the stacking shaft opposite the supply side not through the stacking shaft. If so required, the device also comprises means for interrupting the supply stream of flat articles.